CN102709797B - Intermediate infrared cascaded pulse optical fiber laser - Google Patents

Abstract

The invention relates to a mid-infrared cascaded pulsed fiber laser, comprising sequentially connected semiconductor lasers, a coupling lens group and a double-clad ZBLAN fiber, characterized in that the dichroic mirror is located in the coupling lens group, and the double-clad Fiber Bragg grating FBG ₁ 4 and fiber Bragg grating FBG ₂ 5 are arranged between one end of the ZBLAN fiber and the coupling lens group, and the other end of the ZBLAN fiber is provided with a wide-spectrum reflector, and the wide-spectrum reflector is close to the double cladding The surface of one side of the ZBLAN fiber has a graphene film used as a saturable absorber for the laser light. The fiber Bragg grating FBG ₁ and the wide-spectrum reflector constitute the first resonant cavity of the laser, while the fiber Bragg grating FBG ₂ 5 and the broad-spectrum reflector constitute the second resonant cavity of the laser. The beneficial effects of the invention are: the device has a simple structure, high portability and integration, and is beneficial to practical application.

Description

A mid-infrared cascade pulsed fiber laser

technical field

The invention belongs to the field of laser technology, in particular to a pulse fiber laser.

Background technique

Fiber laser has significant advantages such as low laser threshold, good output beam quality, high conversion efficiency, high "surface area/volume" ratio, good flexibility and flexibility, and easy integration. In the recent research of pulsed fiber lasers, its wavelength is mainly The concentration is around 2.8um, and the methods adopted are mainly gain modulation, active Q-switching of acousto-optic modulator and passive Q-switching of saturable absorber. 1. The gain modulation method is to periodically modulate the number of particles in the energy level of the laser transition through the pulse pumping method to realize the pulse output of the laser, but this method requires pulse modulation of the pump light, which is easy to damage the pump laser and fiber end faces. 2. The active Q-switching of the acousto-optic modulator is to control the loss in the laser cavity by placing the acousto-optic modulator outside the fiber and in the resonant cavity to achieve the output of the Q-switched pulse. This method requires placing an acousto-optic modulator outside the fiber. Modulator, which makes the fiber laser lose its inherent advantages of flexibility, compactness, and small size. In addition, the acousto-optic modulator in the mid-infrared band requires special materials, which increases its production cost and difficulty. 3. As for the passive Q-switching method of saturable absorbers, no saturable absorbers working in the band around 2.8um have been developed in the world.

Contents of the invention

The present invention proposes a mid-infrared cascaded pulsed fiber laser to solve the shortcomings of the pulsed fiber laser in the prior art.

The technical solution of the present invention is: a mid-infrared cascaded pulsed fiber laser, comprising sequentially connected semiconductor lasers, coupling lens groups and double-clad ZBLAN optical fibers, characterized in that the dichroic mirror is located in the coupling lens group, the A fiber Bragg grating FBG ₁₄ and a fiber Bragg grating FBG ₂ 5 are arranged between one end of the double-clad ZBLAN fiber and the coupling lens group, and the other end of the ZBLAN fiber is provided with a wide-spectrum reflector, and the wide-spectrum reflector The surface near the side of the double-clad ZBLAN fiber has a graphene film used as a saturable absorber for laser light.

The fiber Bragg grating FBG ₁ and the wide-spectrum reflector constitute the first resonant cavity of the laser, while the fiber Bragg grating FBG ₂ 5 and the broad-spectrum reflector constitute the second resonant cavity of the laser.

The double-clad ZBLAN fiber is a double-clad Er ³⁺ -doped ZBLAN fiber, and the Er ³⁺ ion level transitions in the double-clad Er ³⁺ -doped ZBLAN fiber correspond to the transitions of lasers with wavelengths of 1.6 μm and 2.7 μm respectively radiation.

The fiber Bragg grating FBG ₁ and the fiber Bragg grating FBG ₂ are written on the double-clad Er ^{3+ -doped} ZBLAN fiber by a femtosecond laser, and the reflection center wavelength of the fiber Bragg grating FBG ₁ 4 corresponds to 1.6 μm, and to The 1.6 μm laser has a high reflectivity, and the reflection center wavelength of the fiber Bragg grating FBG ₂ 5 corresponds to 2.7 μm, but it has a relatively high transmittance to the 2.7 μm laser.

The double-clad ZBLAN fiber is a double-clad doped or Ho ³⁺ ZBLAN fiber, and the Ho ³⁺ ion energy level transitions in the double-clad Ho ^3+-doped ZBLAN fiber correspond to lasers with wavelengths of 2.1 μm and 3.0 μm respectively. jump radiation.

The fiber Bragg grating FBG ₁ and the fiber Bragg grating FBG ₂ are written on the double-clad Ho ^{3+ -doped} ZBLAN fiber by a femtosecond laser, and the reflection center wavelength of the fiber Bragg grating FBG ₁ 4 corresponds to 2.1 μm, and to The 2.1 μm laser has a high reflectivity, and the reflection center wavelength of the fiber Bragg grating FBG ₂ corresponds to 3.0 μm, but it has a relatively high transmittance to the 3.0 μm laser.

The beneficial effects of the present invention are: 1. It avoids the need to pulse modulate the pump light in the traditional gain modulation method and the active Q-switching method of the acousto-optic modulator, thereby causing damage to the pump laser and the end face of the optical fiber, and using an external The acousto-optic modulation device placed outside the optical fiber causes problems such as reduced flexibility of the device, which makes the device simple in structure, high in portability and integration, and is beneficial to practical applications. 2. It avoids the problem that there is no saturable absorber in the band around 2.8 μm in the passive Q-switching method.

Description of drawings

Fig. 1 is a schematic structural diagram of a mid-infrared cascaded pulsed fiber laser according to the present invention.

Fig. 2 is a schematic diagram of the energy level change of the double-clad ZBLAN fiber of the present invention.

Explanation of reference signs: 1 semiconductor laser, 2 coupling lens group, 3 dichroic mirror, 4 fiber Bragg grating FBG ₁ , 5 fiber Bragg grating FBG ₂ , 6 double-clad ZBLAN fiber, 7 graphene film, 8 wide-spectrum reflector , 9 energy level ⁴ I _11/2 or ⁵ I ₆ , 10 energy level ⁴ I _13/2 or ⁵ I ₇ , 11 energy level ⁴ I _15/2 or ⁵ I ₈ , 12 for 2.7 μm or 3.0 μm laser, 13 1.6μm or 2.1μm laser, 14 continuous pump light.

Detailed ways

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings and specific examples.

Embodiment 1: As shown in Figure 1, a mid-infrared cascade pulsed fiber laser, including a semiconductor laser 1, a coupling lens group 2 and a double-clad ZBLAN (fluoride) fiber 6 connected in sequence, the dichroic mirror 3 Located in the coupling lens group 2, a fiber Bragg grating FBG ₁ 4 and a fiber Bragg grating FBG ₂ 5 are arranged between one end of the double-clad ZBLAN fiber 6 and the coupling lens group 2, and the other end of the ZBLAN fiber 6 is provided with A broad-spectrum reflector 8, the surface of the broad-spectrum reflector 8 near the double-clad ZBLAN fiber 6 has a graphene film 7 used as a saturable absorber for laser light.

The double-clad ZBLAN fiber 6 is a double-clad Er ³⁺ -doped ZBLAN fiber, and the Er ³⁺ ion energy level transitions in the double-clad Er ³⁺ -doped ZBLAN fiber correspond to lasers with wavelengths of 1.6 μm and 2.7 μm respectively. jump radiation.

The graphene film 7 is formed on the surface of the wide-spectrum mirror by depositing a graphene-polyvinyl alcohol (graphene-PVA) solution, as a saturable absorber for 1.6 μm laser light.

The fiber Bragg grating FBG ₁ 4 and the wide-spectrum reflector 8 constitute the first resonant cavity of the laser, while the fiber Bragg grating FBG ₂ 5 and the broad-spectrum reflector 8 constitute the second resonant cavity of the laser. The central wavelength of the first resonant cavity is 1.6 μm, and the central wavelength of the second resonant cavity is 2.7 μm.

The fiber Bragg gratings FBG ₁ 4 and fiber Bragg gratings FBG ₂ 5 are written on the double-clad Er ³⁺ (erbium ion) ZBLAN fiber by a femtosecond laser, and the reflection center wavelengths of the fiber Bragg gratings FBG ₁ 4 correspond to The fiber Bragg grating FBG ₂ 5 has a reflection center wavelength corresponding to 2.7 μm, but it has a higher transmittance to the 2.7 μm laser.

In this embodiment, the semiconductor laser 1 is used as a pumping source, which can output continuous pumping light with a wavelength of 975 nm. The coupling lens group 2 is used to collimate the continuous pumping light, and couple it into the inner cladding of the double-clad Er3 ^+-doped ZBLAN fiber 6; the dichroic mirror 3 has a high transmittance to the continuous pumping light It has high reflectivity for the generated 2.7μm laser, and can be used as the output coupling of pulsed laser. The wide-spectrum reflector 8 serves as one end of the resonant cavity and has the characteristic of high reflectivity for 1.6 μm and 2.7 μm lasers.

Embodiment 2: as shown in Figure 1, the structure of the present embodiment is identical with embodiment 1, and difference is that described double-clad ZBLAN optical fiber 6 adopts double-clad doped with Ho ³⁺ ZBLAN optical fiber, therefore, corresponding described The Ho ³⁺ ion level transitions in double-clad Ho ^{3+ -doped} ZBLAN fibers correspond to the transition radiation of lasers with wavelengths of 2.1 μm and 3.0 μm, respectively.

The graphene film 7 is formed on the surface of the wide-spectrum mirror by depositing a graphene-polyvinyl alcohol (graphene-PVA) solution, as a saturable absorber for 2.1 μm laser light.

The fiber Bragg grating FBG ₁ 4 and the wide-spectrum reflector 8 constitute the first resonant cavity of the laser, while the fiber Bragg grating FBG ₂ 5 and the broad-spectrum reflector 8 constitute the second resonant cavity of the laser. The central wavelength of the first resonant cavity is 2.1 μm, and the central wavelength of the second resonant cavity is 3.0 μm.

The fiber Bragg gratings FBG ₁ 4 and fiber Bragg gratings FBG ₂ 5 are written on the double-clad Ho ³⁺ (holmium ion) ZBLAN fiber by a femtosecond laser, and the reflection center wavelengths of the fiber Bragg gratings FBG ₁ 4 correspond to The fiber Bragg grating FBG ₂ 5 has a reflection center wavelength corresponding to 3.0 μm, but it has a higher transmittance to the 3.0 μm laser.

In this embodiment, semiconductor laser 1 is used as a pumping source, which can output continuous pumping light with a wavelength of 1150 nm. The coupling lens group 2 is used to collimate the continuous pumping light, and couple it into the inner cladding of the double-clad Ho ³⁺ doped ZBLAN fiber 6; the dichroic mirror 3 has a high transmittance to the continuous pumping light It has high reflectivity for the generated 3.0μm laser, and can be used as the output coupling of pulsed laser. The wide-spectrum reflector 8 is used as one end of the resonant cavity, and has the characteristic of high reflectivity for 2.1 μm and 3.0 μm lasers.

Below, in conjunction with accompanying drawing 2, the operating principle of embodiment 1 and embodiment 2 is described further:

The continuous pumping light with a wavelength of 975nm generated by the semiconductor laser 1 is collimated through the coupling lens group 2 and coupled into the inner cladding of the double-clad Er ³⁺ doped ZBLAN (fluoride) fiber 6, in the fiber Bragg grating FBG ₁ 4 The continuous laser light of 1.6 μm is generated in the resonant cavity formed by the wide-spectrum mirror 8, corresponding to the energy level transition of ⁴ I1 _3/2 → ⁴ I1 _5/2 (that is, the number 10 to the number 11 in Figure 2), in the graphene Under the saturated absorption of 7, graphene 7 passively Q-switches the 1.6 μm continuous laser, thus generating a 1.6 μm pulsed laser. At the same time, the formed 1.6 μm pulsed laser periodically modulates the number of inversion particles from ⁴ I _11/2 → ⁴ I _13/2 (namely 9 to 10 in Figure 2), that is, to ⁴ I _{11 /2} → ⁴ I _13/2 energy level transition corresponding to the laser gain modulation, so a pulsed laser with a wavelength of 2.7 μm is generated, which resonates in the resonant cavity formed by FBG ₂ 5 and broadband mirror 8 and is amplified , and finally output a pulsed laser with a wavelength of 2.7 μm through the dichromatic mirror 3 .

In the above embodiments, the semiconductor laser with a wavelength of 975nm is used, and the corresponding double-clad Er ³⁺ doped ZBLAN (fluoride) fiber is used; the semiconductor laser with a wavelength of 1150nm can also be used, and the corresponding one is Double-clad Ho ³⁺ doped ZBLAN (fluoride) fiber, at this time, the corresponding energy levels are ⁵ I ₆ , ⁵ I ₇ , ⁵ I ₈ ; the wavelength of the generated pulsed laser is 2.1 μm ( ⁵ I ₇ → ⁵ I ₈ energy level transition) and 3.0μm ( ⁵ I ₆ → ⁵ I ₇ energy level transition), the output is 3.0um pulsed laser.

Although the above two embodiments have only given two kinds of differently doped double-clad ZBLAN optical fibers 6, and the wavelengths corresponding to these two differently doped double-clad ZBLAN optical fibers 6 are 975nm and 1150nm as pumps. Pu source, thus producing corresponding two kinds of differently doped transition radiation, two kinds of central wavelengths of the first resonant cavity and the second resonant cavity and different optical properties of fiber Bragg gratings FBG ₁ 4 and fiber Bragg gratings FBG ₂ 5 , those of ordinary skill in the art should realize that the innovation of the application of the present invention lies first in the structure itself, and second in the specific doping and values of the two embodiments, which appear only for better illustration The structural principles of the present invention should not be construed as limiting the application of the present invention.

Claims (6)

1. cascaded infrared pulse optical fiber in a kind, comprise the semiconductor laser (1), coupled lens group (2) and the double clad ZBLAN optical fiber (6) that connect successively, it is characterized in that, also comprise dichroic mirror (3), described dichroic mirror (3) is arranged in coupled lens group (2), between one end of described double clad ZBLAN optical fiber (6) and coupled lens group (2), is provided with optical fiber bragg grating FBG ₁and optical fiber bragg grating FBG (4) ₂(5), the other end of described ZBLAN optical fiber (6) is provided with wide range speculum (8), and described wide range speculum (8) has graphene film (7) as the saturable absorber of laser near the surface of a side of double clad ZBLAN optical fiber (6).

According to claim 1 a kind of in cascaded infrared pulse optical fiber, it is characterized in that described fine bragg grating FBG ₁(4) and wide range speculum (8) form the first resonant cavity of laser, and optical fiber bragg grating FBG ₂(5) and wide range speculum (8) form the second resonant cavity of laser.

According to claim 1 and 2 a kind of in cascaded infrared pulse optical fiber, it is characterized in that, described double clad ZBLAN optical fiber (6) is mixed Er for double clad ³⁺zBLAN optical fiber, described double clad is mixed Er ³⁺er in ZBLAN optical fiber ³⁺ion energy level transition respectively corresponding wavelength is the transition radiation of 1.6 μ m and 2.7 μ m laser.

According to claim 3 a kind of in cascaded infrared pulse optical fiber, it is characterized in that described optical fiber bragg grating FBG ₁and optical fiber bragg grating FBG (4) ₂(5) by femto-second laser, in described double clad, mix Er ³⁺on ZBLAN optical fiber, inscribe and form, optical fiber bragg grating FBG ₁(4) reflection kernel wavelength is corresponding to 1.6 μ m, and 1.6 μ m laser are to high reflectance, described optical fiber bragg grating FBG ₂(5) reflection kernel wavelength is corresponding to 2.7 μ m, but it has higher transmissivity to 2.7 μ m laser.

According to claim 1 and 2 a kind of in cascaded infrared pulse optical fiber, it is characterized in that, described double clad ZBLAN optical fiber (6) is mixed Ho for double clad ³⁺zBLAN optical fiber, described double clad is mixed Ho ³⁺ho in ZBLAN optical fiber ³⁺ion energy level transition respectively corresponding wavelength is the transition radiation of 2.1 μ m and 3.0 μ m laser.

According to claim 5 a kind of in cascaded infrared pulse optical fiber, it is characterized in that described optical fiber bragg grating FBG ₁and optical fiber bragg grating FBG (4) ₂(5) by femto-second laser, in described double clad, mix Ho ³⁺on ZBLAN optical fiber, inscribe and form, optical fiber bragg grating FBG ₁(4) reflection kernel wavelength is corresponding to 2.1 μ m, and 2.1 μ m laser are to high reflectance, described optical fiber bragg grating FBG ₂(5) reflection kernel wavelength is corresponding to 3.0 μ m, but it has higher transmissivity to 3.0 μ m laser.

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